Computer disk drives store information on magnetic disks. Typically, the information is stored on each disk in concentric tracks that are divided into sectors. Information is written to and read from a disk by a transducer that is mounted on an actuator arm capable of moving the transducer radially over the disk. Accordingly, the movement of the actuator arm allows the transducer to access different tracks. The disk is rotated by a spindle motor at high speed which allows the transducer to access different sectors on the disk.
A conventional disk drive, generally designated 10, is illustrated in FIG. 1. The disk drive comprises a disk 12 that is rotated by a spin motor 14. The spin motor 14 is mounted to a base plate 16.
The disk drive 10 also includes an actuator arm assembly 18, which includes a transducer 20 (wherein the transducer has both a write head and a read head) mounted to a flexure arm 22. The actuator arm assembly 18 is attached to an actuator arm 24 that can rotate about a bearing assembly 26. A voice coil motor 28 cooperates with the actuator arm 24 and, hence, the actuator arm assembly 18, to move the transducer 20 relative to the disk 12. The spin motor 14, voice coil motor 28 and transducer 20 are coupled to a number of electronic circuits 30 mounted to a printed circuit board 32. The electronic circuits 30 typically include a read channel chip, a microprocessor-based controller and a random access memory (RAM) device.
The disk drive 10 typically includes a plurality of disks 12 and, therefore, a plurality of corresponding actuator arm assemblies 18. However, it is also possible for the disk drive 10 to include a single disk 12 as shown in FIG. 1.
FIG. 2 is a functional block diagram which illustrates a conventional disk drive 10 that is coupled to a host computer 33 via an input/output port 34. The disk drive 10 is used by the host computer 33 as a data storage device. The host 33 delivers data access requests to the disk drive 10 via port 34. The port 34 is also used to transfer customer data between the disk drive 10 and the host 33 during read and write operations.
In addition to the components of the disk drive 10 shown and labeled in FIG. 1, FIG. 2 illustrates (in block diagram form) the disk drive's controller 36, read/write channel 38 and interface 40. Conventionally, data is stored on the disk 12 in substantially concentric data storage tracks on its surface. In a disk drive 10, for example, data is stored in the form of magnetic polarity transitions within each track. Data is “read” from the disk 12 by positioning the transducer 20 (i.e., the transducer's read head) above a desired track of the disk 12 and sensing the magnetic polarity transitions stored within the track, as the track moves below the transducer 20. Similarly, data is “written” to the disk 12 by positioning the transducer 20 (i.e., the transducer's write head) above a desired track and delivering a write current representative of the desired data to the transducer 20 at an appropriate time.
The actuator arm assembly 18 is a semi-rigid member that acts as a support structure for the transducer 20, holding it above the surface of the disk 12. The actuator arm assembly 18 is coupled at one end to the transducer 20 and at another end to the VCM 28. The VCM 28 is operative for imparting controlled motion to the actuator arm 18 to appropriately position the transducer 20 with respect to the disk 12. The VCM 28 operates in response to a control signal icontrol generated by the controller 36. The controller 36 generates the control signal icontrol in response to, among other things, an access command received from the host computer 33 via the interface 40.
The read/write channel 38 is operative for appropriately processing the data being read from/written to the disk 12. For example, during a read operation, the read/write channel 38 converts an analog read signal generated by the transducer 20 into a digital data signal that can be recognized by the controller 36. The channel 38 is also generally capable of recovering timing information from the analog read signal. During a write operation, the read/write channel 38 converts customer data received from the host 32 into a write current signal that is delivered to the transducer 20 to “write” the customer data to an appropriate portion of the disk 12. The read/write channel 38 is also operative for continually processing data read from servo information stored on the disk 12 and delivering the processed data to the controller 36 for use in, for example, transducer positioning.
FIG. 3 is a top view of a magnetic storage disk 12 illustrating a typical organization of data on the surface of the disk 12. As shown, the disk 12 includes a plurality of concentric data storage tracks 42, which are used for storing data on the disk 12. The data storage tracks 42 are illustrated as center lines on the surface of the disk 12; however, it should be understood that the actual tracks will each occupy a finite width about a corresponding centerline. The data storage disk 12 also includes servo information in the form of a plurality of radially-aligned servo spokes 44 that each cross all of the tracks 42 on the disk 12. The servo information in the servo spokes 44 (also known as servo sectors) is read by the transducer 20 during disk drive operation for use in positioning the transducer 20 above a desired track 42 of the disk 12. Among other things, the servo information includes a plurality of servo bursts (e.g., A, B, C and D bursts or the like) that are used to generate a Position Error Signal (PES) to position the write head relative to a track's centerline during a track following operation. The portions of the track between servo spokes 44 have traditionally been used to store customer data received from, for example, the host computer 33 and are thus referred to herein as customer data regions 46.
It should be understood that, for ease of illustration, only a small number of tracks 42 and servo spokes 44 have been shown on the surface of the disk 12 of FIG. 3. That is, conventional disk drives include one or more disk surfaces having a considerably larger number of tracks and servo spokes.
During operation, disk drives may be subjected to disturbances such as shocks and vibrations. Shocks may generally be due to external forces, while vibrations may generally be due to both external and internal forces. For example, a shock can occur when someone or something bumps the disk drive (or the housing containing the disk drive). External vibrations may be due to, for example, an attached cooling fan or nearby disk drives performing seek operations. Internal vibrations may be due to seek operations and/or movement of other components within the disk drive.
Because the transducer's position is only corrected when a servo sector is encountered, there is a risk that shocks and vibrations can cause off-track writes. That is, shocks and vibrations can cause data to be written: (1) at improper locations such that data in nearby tracks (usually adjacent tracks) is overwritten; or, (2) so far away from the data's intended location that it cannot be properly read (i.e., it is irrecoverable).
One prior method of reducing off-track writes uses a shock sensor comprising an accelerometer that is mounted on the printed circuit board 32. However, using an accelerometer has a number of disadvantages (only some of which are mentioned herein).
Specifically, an accelerometer, since it is an off-the-shelf component, adds cost to the disk drive 10. Accordingly, it would be beneficial to develop a method and apparatus for reducing off-track writes which does not require any additional components, such as an accelerometer.
It should be understood that disk drives are expected to withstand a certain level of shock or vibration without writing off-track. “Safe shocks” are shocks which would not result in an off-track write, while “unsafe” shocks are shocks which would result in an off-track write. Similarly, “safe vibrations” are vibrations which would not result in an off-track write, and “unsafe vibrations” are vibrations which would result in an off-track write.
When a shock or vibration occurs, an accelerometer outputs an analog signal which (after filtering) is compared to a predetermined threshold. If the threshold is exceeded (or, in another case, not met), an off-track event is likely to occur and any write operations are prohibited, generally, for one revolution. Next, the output of the accelerometer is again compared to the predetermined threshold. If the output of the accelerometer is less than (or, in another case, greater than) the predetermined threshold, the write operation is allowed to be performed.
Determination or “tuning” of the predetermined threshold is performed using an iterative technique. Because it is extremely time-consuming to determine individual predetermined thresholds for each drive, a predetermined threshold is determined for a group of drives (generally, on a product-line by product-line basis).
A “false trigger” can occur when the disk drive believes that a “safe shock” or “safe vibration” is an “unsafe shock” or “unsafe vibration.” For example, in the case of an accelerometer, a false trigger can occur when the output of the accelerometer is greater than the predetermined threshold, but an off-track write would not actually occur due to the shock or vibration that is being measured by the accelerometer. Because false triggers can reduce a disk drive's performance (due to, for example, write operations being prohibited for one revolution), it is important that false triggers are kept to a low level.
Accelerometers can cause an undesirable number of false triggers due to output variations between individual accelerometers. That is, a first accelerometer mounted to a printed circuit board that is subjected to a shock may output a signal that is different from the signal output by a second accelerometer (of the same brand, type and model as the first accelerometer) mounted identically to the printed circuit board when subjected to the same shock. This makes tuning of the predetermined threshold extremely difficult and, therefore, can cause a large number of false triggers, thereby negatively impacting drive performance. Accordingly, it would be desirable to develop a method and apparatus for reducing off-track writes which does not cause a large number of false triggers.
In order to ensure that disk drives are capable of properly handling shocks and vibrations, disk drives are subjected to a battery of qualification tests. If a drive fails to meet the shock and vibration qualification tests, the drive may be scrapped or a line of disk drives may be required to be redesigned, thereby increasing manufacturing costs and/or reducing manufacturing throughput. Accordingly, it would be desirable to design a method and apparatus for reducing off-track writes, which meets shock and vibration qualification tests more effectively than prior techniques.